The present invention relates to a semiconductor device having a field-effect transistor using a nitride semiconductor layer and a method for manufacturing the same.
Field-effect transistors using a nitride semiconductor layer made of GaN and the like have characteristics of high withstand voltage and low resistance, so that the transistors are expected to be used for elements for electric power control.
Patent document 1 describes that, over a channel layer made of GaN, an electron supply layer made of AlGaN is formed, and a gate insulating film made of AlN and a cap layer are further stacked over the electron supply layer in this order. The cap layer is made of a material having the same lattice parameter or thermal expansion coefficient as a barrier layer or the electron supply layer.    Patent Document 1    Japanese Patent Application Publication No. 2008-140813